


Project Arrhythmia: Black Heart One-Shots

by Taffyness559



Category: Black Heart - Fandom, Project Arrhythmia, Project Arrhythmia: Black Heart
Genre: Anthropomorphism - Freeform, During Canon, Fanfiction, Gen, Other, Pre-Canon, object heads - Freeform, semi-canon, shapeheads
Language: English
Status: In-Progress
Published: 2020-12-26
Updated: 2021-01-01
Packaged: 2021-03-10 16:48:37
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 4,082
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28330395
Author URL: https://archiveofourown.org/users/Taffyness559/pseuds/Taffyness559
Summary: A collection of one-shots I've written for Ol666's Black Heart series for Project Arrhythmia. Everything here is my interpretation of canon characters and events. Since the series isn't very well defined, details are very loose and may change from story to story, as I tend to change headcanons a lot. Regardless, I hope y'all enjoy!
Relationships: Nautilus / Aura
Kudos: 3





	1. Break-In

**Author's Note:**

  * Inspired by [Project Arrhythmia: Black Heart (Chapter 1)](https://archiveofourown.org/external_works/731619) by ol666. 



> This takes place a while before the events of Black Heart. Nautilus, a thief from a town down the mountain, attempts to steal some food from a castle carved into the mountain. However, he meets a threatening foe, or so she seems.

Nautilus looked up at the mansion jutting out from the sheer cliff wall. He panted, body drenched in sweat. An hour’s worth of climbing would be worth the trouble, however. At least, that’s what he told himself. Taking in a breath of the cool night air, he got up from the ledge he sat on and began climbing again.

“Just a few more feet,” He panted. His boot slid, loosening a rock from under him. Reflexes kicked in and adjusted his foot to keep hold. He froze. The rock clattered down the cliff edge, but it remained to be the only sound. He sighed. Last thing he wanted now was to get caught. The crystalline people of the mountains were notorious for having strict punishments for intruders. He continued climbing and kept his gaze fixed on the window just above. Just a few more feet...

——

Aura leaned back in her chair and groaned. Her eyes ached and her head throbbed. Insomnia settled in, clashing against her body’s desire for sleep. Every effort to rest ended in restless tossing and turning, but the very effort to use her energy for productivity was all for naught. The words swam about the pages. A language she knew by heart looked foreign and strange to her in that moment. She ran her fingers through her plum-colored curls. The glittering strands shifted in the flickering light. She looked at the clock next to her desk. Its hands pointed to three o’clock. She rubbed her temple and groaned.

“I should be doing more than just wallowing in my frustration...” She grumbled. The book in front of her only stared back, its words just as indecipherable as ever. Aura sighed. She laid her face down on the pages. The coolness of the book was refreshing, at least.

_Creaaaak..._

Aura jolted and turned to the door. It was much too late for her parents to be up, or anyone else for that matter. Thinking fast, she dimmed the lights in her room with a swift wave of her hand. Leaping up from her chair and recovering from the sudden head rush of standing, she crept towards the door and creaked it open to look out into the hall.

It was as dark as ever. Hues of violet and dark blue tinted the walls, casting everything in a monochrome hue. She peeked out more, letting her head go past her door. That was when she noticed one window hung open. The curtains drifted in the slight breeze like a ghost. She stared. _Those... shouldn’t be open,_ she thought. Just then, she heard someone climbing up to the window. She gasped and hid behind her door. Another wave of her hand, and her lights were out, casting her into darkness. She scanned her room up and down. Her wand laid on her desk. To be safe, she took another look out of her door but was careful not to open it too much.

A dark shadow filled the open window. The intruder grunted as he hoisted himself up over the ledge. He flopped onto the ledge, panting and huffing like he had run a marathon. Aura reached her hand behind her and focused, her attention now razor sharp. Her wand jolted towards her hand. She caught it in a practiced manner and continued to watch the intruder.

After laying in the window and scouting out the hall for anyone watching, he crawled in, coming close to falling in and giving himself away before rolling out onto the ground. He was a hefty figure, a large pot-belly sitting between his legs as he sat up, still panting somewhat. In the light coming from the window, his toned arms gleamed with a soft pale blue shine. He stood strangely, and for a moment, Aura believed his legs were backwards. Watching him wander around the hall, she realized that he was digitigrade. The intruder murmured to himself before wandering off in the opposite direction of Aura. Judging by how he moved, he looked more curious and lost than an actual threat. Aura took no chances, however, and she followed close behind, her wand at the ready.

Whoever was in her house, they didn’t seem too dangerous. That was a relief. Aura watched him as he wandered about, muttering and looking down corridors. He seemed less interested in anything of value around, making Aura more and more curious about what it was he wanted. He passed by the kitchen and did a double take. She could make out a soft “Fuck yeah,” before the figure bee-lined in. This only served to further confuse her. _There’s not anything valuable in there... is there?_ She crept towards the kitchen. Rustling and creaking came from the room. She peeked in to see the man rummaging around in the pantry. The window in the room illuminated him, allowing her to see the man in full form. Indigo scales covered him, save for his head, which was a cube. Large, clawed paws nudged past opened boxes and touched food. They grabbed food with a surreal grace and stuffed the goods into his large pockets on his baggy pants. He seemed to have cut his shirt open to expose his sides, and she spotted a set of gills that twitched every so often.

Aura shook her head and backed away from the door. _There’s a thief in here!_ She scolded herself. _Don’t just stare at him, do something_! She was about to step in when she heard his footsteps coming towards the door. Despite herself, she shrank back into the shadows. She hid behind a hope chest in the hall right as he stepped out. She peeked over the edge of the chest, watching him walk down the hall away from her. Her hand clenched around her wand. She floated off of the ground, making sure to not make a sound as she followed, wand at the ready. The thief, having had what he wanted, wandered about. Finally, he reached a dead end and grunted. Aura lowered herself to the ground. She stood in the middle of the hall, her stance wide. Her mind raced as she came closer to the thief as he looked for a way out. His wide stature intimidated her. _He’d take me out in an instant, she thought. There’s no way in hell!_

The thief grunted. “Hm, I coulda sworn there was a door here...” He shrugged and turned. He looked up from the floor and froze. Aura stared him in the eyes as she too locked up. His eyes... glowed. The yellowed sclera gave off a faint glow, only making the shrinking of his pupils more apparent. Aura clenched her wand tighter. Her legs trembled under her. She prayed he didn’t notice her fear.

——

Nautilus stared back at the young woman who had appeared behind him. A lump formed in his throat. _Shit._ He opened his mouth to speak, but only a squeak came out as she jolted, her wand pointed straight at him. “H-Hey! Wait, I ai—woah!” Nautilus attempted to back away, but he fell over. He scooted backwards, covering his face with his arm. The woman pointed her wand at him.

“Who are you, and what are you doing here?” She said. Her voice quivered, but her stance was dominant. Nautilus gazed up at her from under his arm and gulped.

She was... _pretty!_ Even though she looked tired and frazzled, she still maintained a regal air. Her hair was a plum-colored sky with twinkling stars. It curled in on itself in loose coils and strands, creating a flowing cascade which rested on her shoulders. Her crystal skin shone in the shifting light. Her nightgown fell over her thin, graceful frame. He felt his cheeks warm as he opened his mouth.

“I-I... uh... I...” He stuttered. The woman’s expression faltered before she stiffened again. She was putting on a brave face, but he didn’t care. He lost himself in her tanzanite eyes.

“I said, who are you?” She asked, her voice firm. Nautilus snapped out of his trance, remembering that he was an unwelcome visitor. He sputtered.

“Ah, uh! I-I’m Fierro.” He said. A fluttering feeling filled his stomach. The woman cocked her brow.

“Fierro...” She repeated. “Where do you come from?”

  
“J-Just down the mountain,” _Not a complete lie_ , he thought. “I-I live in the... in the woods.”

“What are you doing here?” The woman seemed to relax as she interrogated him, as if it relieved her that she was in control. Nautilus hesitated.

“Well... I was lost,” He started. “I hid my home so well, sometimes I lose track of where it is, and I was being chased by hounds, so I climbed the cliff edge just to get some shelter,” He tapped his claws together. The woman glared down at him.

“... Then why were you stealing food?” She asked. He froze. “Food?” He asked. “I don—“

“Don’t lie to me!” She snapped. “I saw you from the moment you came in. I have the means to get you thrown in prison faster than you can even process what happened!” She traced a glowing sigil in the air and flicked her wand. A cloud of shimmering, periwinkle fog hit him in the face. He flinched as the spell hit him.

“Wh-What the—a-choo!” He sneezed mid sentence, letting a small puff of magic out from his nose. His gills fluttered from the sudden sneeze. He sniffled. “What was that?”

“Truth magic,” She said. “A simple, but effective spell,” She smiled, proud of her achievement before her expression dropped back to a serious look. “Now then, I’ll ask again. Who are you, where are you from, and what are you doing here?” Nautilus blinked, but felt the words climb up his throat.

“N-Nautilus,” He said. He tried to cover his mouth, but the woman waved her wand at him. His arms glowed and pinned against his sides. “Ah! I-I’m from—mmm!” He bit his lip, but the spell was too strong. “—from Seaborough! I ain’t here for much, I just needed some food, that’s it!” He clenched his jaw shut as the words escaped from his throat. The woman loosened her spell, letting him cover his mouth. He scooted back further, cowering.

——

Aura felt a soft pang of guilt as Nautilus shrank away from her. “Nautilus?” She asked. A ring of familiarity sounded in her mind. “Of the... Ballast family?” She cocked her head. Nautilus nodded, then grabbed his head and curled up into a ball with a groan. She lowered her wand and stepped closer. “I thought Seaborough forbade your kin...” She said, crossing her arms. Nautilus looked up at her and sighed.

“They did, but I... kinda live there. If you count living in the woods outside the city as living there,” He grumbled and thumped his paw against his head. “I was hoping you wouldn’t know that, but it looks like those rich assholes can’t keep their damn...” He trailed off, looking up at Aura again, then glancing away. Aura pursed her lips.

“You... needed food, correct?” She asked. Nautilus looked away, blushing harder. He pulled his goggles lower over his face.

“Y-Yeah, the town’s startin’ to get smart,” He said. He tensed and looked up at Aura, his eyes panicked. “P-Please don’t tell on me!” He begged. He got on all fours and kneeled in front of her, hands clasped. She noticed his scarred and calloused hands and chipped tooth. Not only that, but he looked dirty, unlike most residents of the rich seaside town. “I-I hear what your town does to thieves, I ain’t mean any harm, I swear!” He crossed his chest. “You don’t need a spell, you got my word!” He pleaded. Aura back away from him. He looked so small, so desperate. A voice in her head egged her to just tattle on him. _He’ll just come back,_ it growled. B _ut... does he really deserve to being locked up in the stocks and left to die?_ She asked herself. Her expression softened, and she sighed.

“We can stand to lose some food,” She said. Nautilus sighed in relief. “But, you need to go, and fast,” She said. She stepped out of his way. “I suggest you don’t return to your town for at least forty-eight hours. The authorities will track you all the way back home when they find out,” She said, nodding down the hall. Nautilus blinked, his brow furrowing. “... Two days, if that helps,” She said.

“Oh, right,” He chuckled. He stood. Aura noted that up close, he was much shorter than expected. He walked past her and traced his hand against the large dresser next to them.

“A-Again, thank you, I owe ya,” He said. With that, he turned and trotted with little sound down the hall, vanishing around the corner. Aura watched him and sighed. She was about to follow to go back to her room when she spotted something dangling on the dresser door.

A small pocket watch gleamed in the light. Aura stared at it, then picked it up and opened it. It was simple, a cheap one if she were to guess, with only a few tick marks where numbers would be. She examined the inner lid to see the shape of a nautilus shell crudely scratched into the lid. She hovered again and chased after Nautilus. However, when she rounded the corner, she discovered the windows all shut. She opened the one he came in through and looked outside, but there was no trace of him other than the nicks in the stone wall from his claws. She stood, watch clenched in her hands and the cool night breeze hitting her face. She sighed and shut the window.

“I pray you find better fortunes,” She mumbled before turning back to her room, already brewing what she would say when her family noticed the missing food.

——

Nautilus ran through the woods, huffing. The woman’s kindness still had him in shock, but he could barely focus on that. What mattered was getting away. He screeched to a stop in a clearing, his chest heaving from the running. He looked up at the mountain’s cliff-face. The mansion sat silent and brooding. A warm blush graced his cheeks as he smiled.

“What a lady,” He said.


	2. The Failure

**Summary for the Chapter:**

> Nautilus, after letting the target go, is called to Jestar's castle for a chat.

The Failure

Nautilus tromped through the heavy iron doors. He shook the remaining droplets of water from himself, leaving little drops of water on the steps. His hooves clacked against the marble flooring, which reflected his face in its blurry, desaturated surface. He stared at his reflection for a moment. The sensation of water trickling from the sides of his face onto the ground calmed his thumping heart, if only for a moment.

“You do realize you’re still wet, right?” The snarling voice made Nautilus look up to the pillar next to him. In the shadows floated Myst. He leaned against the marble, blending into the milky stone with his pale form. A single dark abyss glared back at him from under long, drooping, white hair. He drifted forwards, but not enough for the light from the open door to hit him.

“Hey Myst,” Nautilus said. “Did you get the message from Jestar too?” Nautilus removed the goggles from his head to check for water droplets.  
  
“Message?” Myst cocked his head a tiny bit too far for comfort. “I didn’t receive any message, no.” Nautilus paused.

“You didn’t? Did…did Puffer? Or Aura?” Nautilus asked as he placed his goggles back on his head. Myst shrugged.

“Not that I know,” he said. “But then again, didn’t you fail to catch Hal?” Myst held his hands together in a faux arm-cross.

“W-Well…” Nautilus started but was interrupted by the low creak of the door across the hole opening. Myst retreated back behind the pillar as a stroke of light filled the room, the massive silver double-door opening on one side. In the doorway, a figure poked his head out and motioned for Nautilus to come forward. Nautilus exchanged glances with Myst, then walked forward.

As Nautilus passed through the doors, he found that the figure in the door had…vanished. A chill went down his spine. He found himself standing in the large chamber, the ceiling arching high above his head into a point like a church. The room was dark, lined with brilliant white stones. An obsidian floor laid below him with a single stripe of quartz leading to the matching throne in the center of the room. Thin grey curtains hanging from the white rafters drifted in the nonexistent wind, but Nautilus couldn’t focus on that. He ran his claws over each other, his steps echoing still. The room was unnaturally cold, and he felt a sense of unwelcomeness in the air. The doors closed shut behind him, making a slam that rang like a gunshot. Nautilus jumped and turned to see no one. He shivered.

“Nautilus.” The voice, comically nasally and shrill, cut through the air, startling the blue cube man again. He turned to the throne, still clasping his claws together. On the throne sat a thin grey figure. He wore a black crown on his head with a black tunic draped over his arms. His limbs were like noodles with no defined joints or bones. He sat reclined in his throne, his legs crossed over one armrest as he held his head in his hand, elbow resting on the other armrest. He inspected his gloved hand as one leg kicked lazily. Nautilus gulped.  
“M-My lor—“  
  
“Come closer, and I told you, just call me Jestar,” Jestar looked at Nautilus with a cynical glare. Nautilus shrank into himself but shuffled forwards to the base of the throne. He bowed halfway, arms stiff at his sides.

“Jestar,” Nautilus said. Jestar grunted, then sat upright. Nautilus straightened and crossed his arms behind his back. Despite having dried himself, Nautilus could feel the precipitation on his head just under his goggles. He thanked the forces above that his goggles were dark. Jestar leaned towards Nautilus and rested his head on the backs of both of his hands, his glowering orange eyes cutting through Nautilus. 

“Do you know why I’ve called you here today?” Jestar asked. Nautilus pursued his lips and glanced at his feet. “Look at me and answer the question.”

“Well, I thought that the others were—“

“It’s a yes or no question, Nautilus.”

“…No,” Nautilus’ eyes glanced to the side. Jestar furrowed his brow and huffed. “Is this about…my last job? Because if it was, it was completely outta my hands!” Nautilus gestured with his hands, elbows locked at his sides. “I mean, you shoulda seen that little bugger, they were so fast, I cou—“

“I know you couldn’t have caught them, that’s why they got away,” Jestar cut Nautilus off. He reclined back in his throne once more. “At least, that’s what you reported.”  
“Yeah, that’s what I reported,” Nautilus clasped his hands. His claws clicked against each other. The room fell silent, the only sounds being Nautilus’ claws clicking and the soft rustle of the curtains above. After a minute, Jestar sighed. 

“Look, Nautilus,” he began. “We both know that your report is…missing some details, so how ‘bout you hack it up?” Nautilus froze up. He resembled a deer in headlights as he snapped his head up to face Jestar.  
“What do you mean?” Nautilus asked. Jestar’s brow furrowed low over his eyes.

“You know what I mean, blockhead! You really don’t think I don’t monitor my assassins?” Jestar shot up to his feet. Nautilus’ heart leaped into his throat and his pine shot a jolt through him. He gulped, a tremor beginning in his body. Jestar groaned as he pressed his temple with two of his fingers. He sat back down on his throne, face still in his hands. “You were so close, you had them in your hands! How could you mess it up?” Jestar’s voice raised. He flung his hands up as if asking for some divine answer to Nautilus’ incompetence. Nautilus bit the corner of his lip.

“I, uh, slipped.” A strained chuckle escaped him. “It’s hard to keep a hold of things with these claws, y’know?” He held up his hands and grinned. His heart thrummed against his chest as his mind screamed for him to run. Jestar’s eyes glowed a bright red.

“Are you serious?” He growled through grit teeth. Nautilus paled. “You absolute idiot! The soul was right in your hands! You couldn’t have just slipped, that’s just…” Jestar trailed off, the burning red eyes flickering with realization. His face dropped to a strange grin; his voice a low growl. “That’s…impossible.” Jestar rose from the throne, his shoulders squared and fists balled. Despite his cartoonish appearance, he loomed over Nautilus’ bulky frame. Jestar stepped down from the throne, glaring at Nautilus still. Nautilus held his hands up in defense as he backed away.

“J-J-Jestar? What are you—“

“Fall to your knees.” Nautilus’ knees buckled and he fell to the floor with a yelp. His weight, as well as the force at which he was forced down, sent spidery cracks out from under him as he landed on his knees. Nautilus tried to crawl away but found he was frozen in place. His chest heaved with labored breaths as Jestar approached. The wicked grin was still plastered on his face. He grabbed Nautilus’ arm and bent it behind his back, making the cowering man squeal. Jestar spun around to his back and forced his other arm behind him as well, twisting them as Nautilus continued to writhe. “I understand what you did now, you let the souls escape.”

“I did no—aUGH!” Nautilus yelled as Jestar formed claws that dug into his wrists. Jestar planted a foot on Nautilus’ back and kicked him down, forcing his face to the floor with enough force to crack the fragile rock below again. Nautilus hissed in a breath as shards of quartz cut into the side of his head. Thankfully, he had enough sense to turn as to avoid his face being hurt. Jestar dug his claws into Nautilus’ wrists, drawing oozing blood the color of midnight.

“You know I don’t like liars, Nautilus,” Jestar growled. His voice rumbled through Nautilus’s head like the roar of thunder. He tried to free his arms, but Jestar only dug deeper. “I’ll spare you if you just say it. I promise,” Jestar cooed. He leaned in closer to Nautilus’ face and contorted his face into a ferocious snarl. “Unlike you, I’m not a filthy liar.” The words dripped from his clenched teeth like poison. Nautilus grit his teeth.

“F-Fine! I let Hal go!” Nautilus shouted. Jestar kicked him over, and Nautilus flopped onto the shattered floor. Nautilus curled up into a ball and rubbed his wrists. Jestar crossed his arms and snarled at the curled-up form.

“There we are, now that wasn’t that hard, was it?” Jestar huffed. Nautilus fought back tears, his wrists burned with fiery ichor and shards of quartz prodding his body. Jestar grabbed him by the collar and pulled him up to his feet. “Stand.” He commanded. Nautilus’ body straightened, but his head continued hanging slack. Jestar held Nautilus’ head up with his hand, his fingers grazing against his cheek. “Now…what do you plan to do about it?”

“I-I…” Nautilus started, but found that he couldn’t think. Jestar smirked.

“You have no plan, do you?” Jestar said. Nautilus was only able to blink. Jestar rolled his eyes, then let Nautilus go, making Nautilus’ knees buckle but maintain balance. Jestar strolled back to his throne. “No worries, I’ve got a plan.” With his back turned, Jestar snapped and pointed back to Nautilus. “Shadows, take him to the dungeons., and get me an update on that locket while you’re at it, will ya?” Before he could process it, Nautilus’ arms were pinned to his sides by a long, thin, shadowy rope. Nautilus snapped out of his trance and snapped his head around. He saw the same shadowy figures he saw earlier. They wrapped thin ropes around him and dragged him back towards the door.

“J-Jestar? Jestar!” Nautilus struggled against his bonds, but was fruitless in his efforts. The last he saw of the chamber was Jestar being handed a scroll. He opened it to reveal plans for some sort of armor.

Jestar looked back at Nautilus and smiled before the doors slammed shut.


End file.
